DbSequence

Action DbSequence allows database sequences to be replicated.

If a single DbSequence action is defined without any parameters for the entire channel (i.e., location group '*') then operations on all database sequences in the capture location(s) that are owned by the current schema will be replicated to all integrate locations. This means that if a nextval is done on the capture database, then after replication a nextval on the target database is guaranteed to return a higher number. However, note that if database sequence 'caching' is enabled in the DBMS, the nextval on the target database may display a 'jump' in values.

The SQL statement CREATE SEQUENCE is also replicated, whereas DROP SEQUENCE is not replicated.

Refresh and Compare also affect any database sequences matched by action DbSequence. Database sequences which are only in the 'write' database are ignored.

Parameters

This section describes the parameters available for action DbSequence.

Following are the two tabs/ways, which you can use for defining action parameters in this dialog:

• Regular: Allows you to define the required parameters by using the UI elements like checkbox and text field.
• Text: Allows you to define the required parameters by specifying them in the text field. You can also copy-paste the action definitions from Data Source Solutions DSS documentation, emails, or demo notes.

Notes for DbSequence

To replicate a specific sequence, use the parameter Name. To replicate all sequences in a schema, use the parameter Schema without Name. To replicate all sequences owned by the current user, do not use either Name or Schema.

Capturing all sequences from multiple schemas cannot be achieved by defining multiple DbSequence actions with parameter Schema but without Name. Instead, you can either define multiple DbSequence actions, each with both parameters Schema and Name, or use multiple capture locations or channels, with each having its own DbSequence action defined with parameter Schema.

Bidirectional Replication

Bidirectional replication of sequences causes problems because the sequence change will 'boomerang back'. This means that after the integrate job has changed the sequence, the DSS capture job will detect this change and send it back to the capture location. These boomerangs make it impossible to run capture and integrate jobs simultaneously. But it is possible to do bidirectional replication for a failover system; i.e. when replication is normally only running from A to B, but after a failover the replication will switch to run from B to A. Immediately after the switchover a single boomerang will be sent from B to A, but afterwards the system will consistent and stable again.

If bidirectional replication is defined, then DSS Refresh of database sequences will also cause a single 'boomerang' to be captured by the target database's capture job.

Session names cannot be used to control bidirectional replication of database sequences in the way that they work for changes to tables. For more information, see Managing Recapturing Using Session Names.

Replication of Sequence Attributes

Database sequence 'attributes' (such as minimum, maximum, increment, randomness and cycling) are not replicated by DSS. When DSS has to create a sequence, it uses default attributes and only the value is set accurately. This means that if a database sequence has non–default attributes, then sequence must be manually created (outside of DSS) on the target database with the same attributes as on the capture database. But once these attributes are set correctly, then DSS will preserve these attributes while replicating the nextval operations.